This invention relates to a fan wheel of a radial fan assembly. More particularly, this invention relates to a single-piece fan wheel for a radial fan in the heating, ventilating and air conditioning system of an automotive vehicle.
In heating, ventilating and air conditioning systems of motor vehicles, the fan wheels of radial fans are driven by small d-c motors. The electric motors have permanent magnets in the stators, while the windings in the rotors are accommodated in open slots. For each revolution of the rotor, the magnitude of the torque delivered pulsates in accordance with the number of slots or a multiple thereof. Accordingly, a slotting frequency or oscillation results which is equal to the number of revolutions per minute times the number of slots in the rotor.
The effect of the torque pulsations on a radial fan with a rigidly mounted fan wheel is to give the wheel a slight radial or tangential relative motion in the rhythm of the slotting frequency. If the fan wheel has in the radial or tangential direction a resonance area, e.g., the fan blades in a radial blower, the slotting frequency becomes audible as a disturbance at a certain rotation speed. The resonance excitation can be minimized by such measures as setting the slots at an angle in the motor. However, the effect of the pulsations in torque cannot be entirely eliminated by such measures.
It has been attempted to place the operating points of radial fans outside of the resonance ranges. With an increasing trend toward regulation, it is necessary, however, to cover the entire range of speed without the production of a hum frequency. To achieve this goal, thin curved spokes have been used as damping elements between the hub and the blade ring of a radial fan, as described in U.S. Pat. No. 4,470,753. The spokes are provided in an intermediate piece which connects the outer surface of the hub to the blade ring. Radial and axial distortions in the spokes due to the aging of the plastic or to centrifugal force results disadvantageously in an increase in the imbalance and, therefore, in an aggravation of the sounds arising from the pulsations in torque.
An object of the present invention is to provide an improved radial fan wheel of the above-described type.
Another object of the present invention is to provide such a fan wheel in which a sound-damping effect continues even after extended periods of operation.